Filter for tobacco smoke



United States Patent 3,255,761 FILTER FOR TOBACCO SMOKE Gunter Reske, Frankfurt am Main, and Joachim Stauif, Bad Soden, Taunus, Germany No Drawing. Filed Mar. 18, 1963, Ser. No. 266,093 2 Claims. (Cl. 13110) The present invention relates to filters for tobacco smoke and more particularly to a filtering substance which absorbs hazardous constituents and improves the taste of the tobacco smoke.

It is generally known that various injuries to health can be caused by inhaling tobacco smoke. In addition to the well known eifect of tobacco smoking on the circulatory system a connection has been proven to exist between the growth of tobacco consumption and the increase of the number of bronchial or lung cancer cases. To avoid these and other dangerous and unwanted efiects of smoking, the use of filters and particularly of cigarette filters has been widely established. Such filters at least partly absorb certain constituents of the tobacco smoke, e.g. nicotine or tobacco tar, and various efforts have been made to develop filters the absorptive properties of which are directed to specific constituents of the smoke. For example carboxymethyl cellulose filters are known which absorb a substantial portion of the tar contained in tobacco smoke.

It is easily possible to manufacture tobacco smoke filters with any degree of absorption. The net result of their filtering action is, however, a thin, relatively flavorless smoke and/or a hard drawing cigarette. Therefore, the properties of the common cigarette filters represent a compromise between absorptive power, taste attenuation, and pressure drop. Furthermore, the commonly used filters do not selectively absorb specific constituents of the smoke but possess a rather general absorptive power which is due to their surface areas.

Also filters have been proposed which are partially or wholly made from proteins. The basic idea concerning these filters is that in the human body certain reactions take place between tobacco smoke and proteins, and that a protein containing filter would presumably be able to trap specifically those smoke constituents which would otherwise react with the proteins of the human organism. No protein filter, however, has come into practical use. We. have made some experiments With protein filters and have found that their pressure drop does not remain constant throughout the smoking of a cigarette but is relatively high at the beginning and relatively low at the end of the smoking process. In practical use are only filters made from cellulose or cellulose derivatives.

Though considerable scientific work in the field of cancer research has been done in the past, it has not yet been possible to identify specific constituents of the tobacco smoke as being responsible for its carcinogenic action.

Various authors have observed that carcinogens are able to destroy or make otherwise ineffective proteinic sulfhydryl groups (SH-.- groups). For example, the observation that the enzymatic action of protein ferments the activity of which is dependent on sulfhydryl groups, is inhibited by cancerogenic agents was reported by E. Gaetani (Tumori, vol. 32, 1946, p. 165), A. Grafi i, H. Kriegel, E. I. Schneider and G. Sydow (Naturwissenschaften, vol. 40, 1953, p. 414), R. Lange (Science, vol. 134, 1961, p. 52), G. C. Mills and J. L. Wood (Cancer Research, vol. 13, 1953, p..69), P. Rondoni and G. P. Barbieri (Enzymologia, vol. 14, 1950, p. and P. Rondoni and M. Bassi (Ricera scient., vol. 18, 1948 p. 1038). According to these observations, it seems to be possible to trace the carcinogenic activity of a given substance by its action on proteinic sulfhydryl groups. In experiments of this kind, it is most convenient to measure the decrease of the virtual SH-- concentration by a physical method.

We have found that beta-lactoglobulin can be conveniently used as a tracer for SH- attacking conditions. Each molecule of beta-lactoglobulin contains several sulfhydryl (SH) groups and several disulfide (SS) groups. If a solution of beta-lactoglobulin in a buffer solution of pH'7 is kept at an elevated temperature, e.g. at C., the molecules react with their SH- and SS groups together and aggregate more and more until finally all the lactoglobulin coagulates. The process of the coagulation of proteins by the application of heat is well known. In the case of beta-lactoglobulin, the aggregation and coagulation takes place, under the stated conditions, via a sulfhydryl reaction mechanism. The growth of the molecules can be observed by their light scattering effect.

For example, we prepared a 0.2 percent by weight solution of beta-lactoglobulin in a phosphate buffer of pH 7. While the solution was keptat 80 C., a light beam of constant intensity was sent through the solution. Due to the formation of aggregates, more and more light is scattered from the solution in the course of the heat aggregation process. A photoelectric system comprising a photocell or photomultiplier was installed with its axis perpendicular to the light beam so that the intensity S of the scattered light could be determined. According to the theory which is not of specific interest here, after a short induction period the change of the scattered light intensity S per unit time t becomes proportional to the square of the initial beta-lactoglobulin concentration 0:

a S/dt=k-c (k is a constant factor of proportionality). Thus, if two equal samples of one and the same beta-lactoglobulin solution are observed under exactly the same conditions, their light scattering curves S=S(t) should be and will be substantially identical. If, however, one of the samples is, before insertion into the light scattering apparatus, treated with a substance or a means which inhibits the normal reactions of the SH groups, a subsequent observation of the light scattering effect will lead to another curve S =S (t) with a diminished slope dS /dt because any molecule the SH groups of which have become ineffective cannot take part in the aggregation process. By means of the above Formula A, a virtual initial concentration c can be calculated from the observed value dS /dt. The ratio of c to the real initial concentration 0 of the untreated solution indicates what proportion of the beta-lactoglobulin has remained unchanged. Consequently, the value indicates the percentage of beta-lactoglobulin molecules which has been damaged by the said pre-treatment, and is a measure of the effectiveness of the pre-treatment.

We have found that tobacco smoke which is drawn through a test volume of the said beta-lactoglo'bulin solution, will inhibit the heat aggregation and the lower the observed values of dS/dt in the same described manner as known carcinogenic means, e.g. ultraviolet light or benzpyrene. According to the present invention, we have also found that tobacco smoke which is drawn through said test volume of said beta-lactoglobulin solution after having passed a filter in which sulfhydryl group containing substances are present, shows the described inhibiting action on the heat aggregation only to a much lesser degree. It is thus clear that filters which contain sulfhydryl group containing substances (hereinafter also referred to (percent) as SH-filters) are apparently effective to absorb the very constituents of the smoke which are the cause of the destructive action on the said beta-lactoglobulin solution.

A suitable filtering material for SH filters according to the invention can be obtained from keratin in the form of wool, hair, horn, or similar raw materials by chemical reduction. Keratin contains numerous disulfide groups (SS groups) which can be reduced to sulfhydryl groups by known processes which will be described later. According to the invention, the use of wool as a raw material is particularly advantageous because its fibrous structure and large surface area is not affected by the reduction process. It is to be noted that keratin which has not been chemically reduced containsno SH groups and will, therefore, not be effective. It is clear that any substance containing SH groups will show more or less the aforedescribed filtering effect; the invention is, therefore, not restricted to the particular materials, conditions, or proportions recited by way of example. Further it is to be noted that the validity of the appended claims is not based on the correctness of the assumption that the smoke constituents retained by the SH filters are actually the carcinogenic constituents, but on the novelty on the disclosed filtering material and its advantageous properties. Of course, it is an advantageous property that the SH filters according to the invention absorb those constituents of the smoke which act on the beta-lactoglobulin test system in the same manner as known carcinogens.

Furthermore, we have found that SH filters according to the invention considerably improve the taste of the smoke. The characteristic tobacco aroma remains unchanged but the taste deteriorating irritations of the mucous membranes are softened.

Also we have found in practical use with cigarettes that the pressure drop of SH filters according to the invention need not be higher than the pressure drop of usual cellulosic filters to make all their advantageous properties fully available, and.that their pressure drop remains substantially constant throughout the whole smoking process.

Accordingly, one of the objects of the present invention is to provide a novel and improved filter of the general kind referred to, which will have a high absorptive power on such smoke constituents which will act destructively on natural proteins.

Another object of the invention is to provide a novel and improved filter which improves the taste of the smoke.

Still another object of the invention is to provide a novel and improved filter which will, in addition to the aforesaid specific absorptive and taste improving properties, have no more draw resistance than filters of the kind known hitherto.

Other and further objects, features, and advantages of the invention will be pointed out hereinafter in the fol-- lowing description of a specific embodiment of the invention.

Properly washed natural wool was treated for 2 hours with a 0.5 molar solution of thioglycolic acid, HSCH COOH, in water at pH 8 and a temperature of 50 C.; the weight ratio was 1 part wool to 75 parts solution. This reduction process has been described more particularly by Schtiberl (Angewandte Chemie, vol. 70, 1958, p. 649), Natural wool contains about 3.35 percent of sulfur, 3.19 percent in the form of disulfide SS-- groups, and 0.15 percent in methionin CSC groups. According to Schoberl, the described reduction process reduce 78 percent of the whole sulfur content to sulfur in SH groups.

After the reduction, the now reduced wool was thoroughly washed and dried in a current of dry nitrogen to avoid back-oxidation. Ordinary filter tip shells of 13 mm. length and 8 mm. diameter were. filled by hand each with about 200 mg. of the dry, reduced wool. Since the wool is normally irregularly crimped, no

mechanical treatment was necessary. The filter tip shells were then attached to a standard brand of cigarettes available on the retail market in Germany by means of an adhesive tape. away from the free end of the filter to obtain a fiat end surface. Thereafter, the weight of the reduced wool in the filters was in the range of 130 to 180 mg. The cigarettes were smoked on a smoking machine the working principle of which was in close agreement with the ordinary process of smoking. Every draw on the cigarette was performed in the following manner: A volume of V=2.4 liters was brought to a slight predetermined vacuum, e.'g. of 0.0l3 atmosphere, and then connected to the suction end of the burning cigarette. Thus air was drawn through the cigarette until atmospheric pressure was re-established in the volume V. In the passageway between the volume V and the suction end of the cigarette, a container with the beta-lactoglobulin test solution could be interposed in known manner by means of valves so that the smoke could be forced through the test solution. Normally, 15 ml. of a 0.2 percent by weight solution of beta-lactoglobulin in a pH 7 buffer were employed. After a certain number of smoke draws, all generated by equal vacua in the volume V, had been drawn through the solution, the solution was brought into the light scattering apparatus already described hereintofore and was heated to a constant temperature of C. The intensity S of the scattered light was measured and plotted against the time t thereby generating the desired S =S (t) curve from which the value of dS /dt was obtained in known manner. After comparison with S=S(t) curves of samples of the solution which had not been treated with the smoke, the value F of Formula B was calculated. This value F is, as has been already explained, a measure of the attack on the sulfhydryl groups and most probably also a relative measure of carcinogenic activity.

Table I shows the results of some typical experiments with cigarettes without filters.

Table I Number of draws through 15 ml. solution (suction pressure Whole cigarette smoked quick1y (no heat aggregation observable). 10. 33. 51.

15 (whole cigarette) Test-s Nos. 1 and 4 show the influence of the combustion velocity.

The following Table II shows results of some other typical experiments in which cigarettes of the same brand were investigated under the same smoking conditions.

Table II Test N 0 Type of filter F (percent) 1 No filter P 2 do 3 150-160 mg. cellulose-acetate filter 51 4 Natural wool, not reduced 48 5 -150 mg. SH filteL 2G 6. do 30 7 21 Superfiuous reduced wool was cut I other natural keratin and of filling a sulfhydryl group containing material into tobacco smoke filters are possible without departing from the spirit and scope of the invention. For example, it is known that also sodium borohydride, NaBH or l-mercapto-ethanol-Z,

can be used as reducing agents, and various machines rfor the automatic production of cigarettes and/or cigarette filters are known which would be suited to manufacture SH filters according to the invention.

What is claimed as new and desired to be secured by Letters Patent is:

1. A cigarette having a filter attached thereto for removing some of the irritating substances from the smoke, said filter comprising a shell containing a charge of a keratinous material selected from the group consisting of wool, hair and horn which have been chemically reduced to provide at least 50% of the available sulphur in the form of sulfhydryl groups.

2. A cigarette having a filter attached thereto ifor removingsorne of the irritating substances from the smoke, said filter comprising a shell containing a charge of from 130 to 180 milligrams of a keratinous material selected from the group consisting of wool, hair andhorn which have been chemically reduced to provide at least 50% of the available sulphur in the form of sulfhydryl groups.

References Cited by the Examiner UNITED STATES PATENTS 606,537 6/1898 Goldenfarb 131-10 2,685,344 8/1954 Bunzl 13110 XR 2,739,033 3/1956 Lubs. 2,928,399 3/1960 Touey 131208 3,030,964 4/1962 Whitmore 131-10 3,019,794 2/ 1962 Whitmore 131--208 FOREIGN PATENTS 13,747 1851 Great Britain.

OTHER REFERENCES SAMUEL KOREN, Primary Examiner.

P. RAY CHAPPELL, ABRAHAM G. STONE,

Examiners.

MELVIN D. REIN, Assistant Examiner.

Biochemische Zeitschrift 331 

1. A CIGARETTE HAVING A FILTER ATTACHED THERETO FOR REMOVING SOME OF THE IRRITATING SUBSTANCES FROM THE SMOKE, SAID FILTER COMPRISING A SHELL CNTAINNG A CHARGE OF A KERATINOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF WOOK, HAIR AND HORN WHICH HAVE BEEN CHEMICALLY REDUCED TO PROVIDE AT LEAST 50% OF THE AVAILABLE SULPHUR IN THE FORM OF SULFHYDRYL GROUPS. 